This invention relates generally to a new process for converting round logs of proper grade into lumber products, primarily dimension lumber. More particularly, it relates to a log cutting and laminating or rejoining process that can readily utilize the smaller diameter logs for converting them to lumber products whereby the yield of lumber from the wood volume in the log is substantially increased.
The centuries old conversion process of sawing logs into lumber results in a very low lumber yield in that, of the total volume of wood in a green log, less than half is or can be converted into usable lumber, primarily because of the constraint that square or rectangular pieces are cut from a cylindrical log. The actual lumber yields utilizing known processes of course vary depending on a number of factors such as log diameter, but even with the best available computer controlled sawing machines the normal yield of lumber from a log is at best sixty percent of the total wood volume. The term lumber is intended to mean that wood product traditionally having the highest marketable value of those products derivable on a longitudinal sawing basis from a log and generally being rectangular in cross section.
The most commonly used log to lumber converting process is that where saws make a plurality of longitudinal cuts through the log with each successive cut generally being in a plane parallel or perpendicular to the previous cut. With this process it is obvious that there are yield limitations simply from the fact that the beginning raw material is cylindrical in nature while the desired final lumber product is rectangular in nature. The wood volume not converted into lumber is utilized in a variety of other ways none of which offer the value of a lumber product. The sawdust can be used as fuel, in particleboard, and the like. The solid wood slabs and edgings can be chipped into small pieces suitable for wood pulp production or likewise they can be used for fuel.
In the past there have been many suggestions of ways to increase the recovery of solid wood products that could be converted from a log. Veneer production and subsequent laminating methods has been one suggestion. In veneer production the cylindrical log is converted into pieces of wood veneer which can then be laminated together to form various wood products. Such composite products and their converting processes do convert more of the wood volume into generally solid wood products, but they still do not generally have the market acceptance of lumber.
The problem of low lumber yields from round logs becomes compounded with the logs have a small diameter which is on the order of from 5-15 inches. The fact is that as the diameter of the logs become smaller a larger percentage of wood volume will necessarily be allocated to sawdust and slabs and edgings. Another factor to be considered, is that as forests are regenerated and harvested the log diameters will, on an overall basis, tend to be smaller when they are ready for breakdown into lumber products.
It thus becomes apparent, in view of the strikingly low lumber yields from present converting processes, that new and improved processes must be conceived and developed to increase the lumber yield from round logs, especially those having a small diameter. Since the demand for lumber products will continue to rise it is essential that processes be developed that can convert a greater amount of round wood volume into lumber.
Such a process should be reasonably simple in order to maintain the high production rates that are necessary in the lumber manufacturing industry. The process comprising the present invention offers simplicity and efficiency in addition to greatly increased yields.
The composite lumber product that is ormed according to the process of the present invention has several characteristics that in fact make it a superior product when compared to traditionally manufactured lumber. In view of the composite nature of the product defects tend to be randomized over the product length by the placement procedure with the individual pieces. An additional advantage in the product results from the orientation of the grain structure of pieces going into the composite product. The cutting step in the process will yield sector or wedge shaped pieces in cross section having three sides. The two faces having longer sides will be comprised of vertical grain while the third face having a shorter side will be comprised of flat grain. Briefly, vertical grain is that grain orientation where the annual rings are generally perpendicular to the particular face while flat grain is that grain orientation where the annular rings are generally parallel to the particular face. Upon drying the sector shaped pieces before the rejoining step it will be recognized by those skilled in the art that cupping of the pieces will be substantially eliminated since the longer sides have vertical grain and only the smaller side has flat grain. The tendency of flat grained wood to cup results because wood shrinks in drying twice as much in a direction tangential to the annular rings as compared to the radial direction. Depending on the grain structure of a particular piece of solid lumber differential shrinkage rates result in distortion in both the cross sectional dimensions and over the length of the piece of lumber.
Because the sector shaped pieces have vertical grain over their longer faces and in view of the manner in which the sectors are rejoined the composite lumber product will likewise have vertical grain over the two longer faces. Consequently all of the lumber products manufactured according to the present invention can have vertical grain over their width dimension. This then results in an improved lumber product because of enhanced dimensional stability as a result of the composite product grain structure. Upon changes in moisture conditions vertical grained lumber will have generally more uniform dimensional changes than a piece of flat grained lumber having the said dimensions.
In terms of flexibility of dimensions for lumber products it is apparent for example that when a log is only 6 inches in diameter 2 inches .times. 10's will not be possible as solid pieces of cut lumber. In the prior art, however, various pressing and gluing processes are available to then make a composite 2 inches .times. 10 inches piece by edge gluing two or more smaller pieces together to yield the desired dimension. While this method does yield larger dimension lumber from smaller diameter logs the resulting composite pieces are generally of nonuniform grain structure and do not have good dimensional stability. With the process of the present invention an edge bonding technique can also be utilized and the resulting dimensioned products do in fact have the uniform grain structures that are necessary for dimensional stability.
Accordingly, from the foregoing, it is apparent that one primary object of the present invention is to convert logs into composite lumber products whereby the percentage of log volume converted to lumber product is substantially increased.
Another primary object of the invention is to manufacture composite lumber products that have improved and more uniform quality.
Yet another main object of the present invention is to convert the logs of generally smaller diameter into composite lumber products.
These primary objects and others will become more apparent and better understood upon reading the following specification in conjunction with the attached drawing.